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Acetaldehyde is the first oxidation product of ethanol in vivo. Our earlier work showed that with sufficient acetaldehyde, five of the six possible sites of the peptide pentalysine were modified as a Schiff base (Braun KP, et al: J Biol Chem 270:11263-11266, 1995). However, we were unable to deduce unequivocally which site was unmodified. Lysine residues, as well as the amine terminal valine residues, in hemoglobin have been implicated as target structures for acetaldehyde adducts resulting from ethanol consumption. Hemoglobin adducts of acetaldehyde have been used clinically as a marker of ethanol consumption, but the chemical nature of these adducts remains undefined. As part of our continuing structural characterization of acetaldehyde-protein adduct formation, we studied the peptides Val-His-Leu-Thr-Pro and Val-His-Leu-Thr-Pro-Val-Glu-Lys, from the amine terminus of the beta-globin chain of hemoglobin, in vitro. Both peptides have at least one potential site for adduct formation. In the octapeptide, the N-terminal amine group of Val as well as the epsilon-amine group of the lysine sidechain can potentially be modified by acetaldehyde. We used mass spectrometry, carbon-13 nuclear magnetic resonance, and Raman spectroscopy and characterized stable Schiff base acetaldehyde adducts of these two peptides at both reactive sites. The identification of stable Schiff base adducts with the N-terminal peptides of the beta-chain of hemoglobin as well as with epsilon-amino groups of lysine provides another possible means of monitoring ethanol consumption. The functional implications of these stable Schiff bases remains undefined.

The depolarized Rayleigh scattering spectra of polypropylene glycol in optically isotropic cyclohexane were studied as a function of polymer molecular weight, concentration, and temperature. The relaxation times were obtained by curve fitting the observed spectra to Lorentzian functions convoluted with the instrumental spectra. By studying the dependence of relaxation times on viscosity, temperature, and concentration and also comparing the results with theoretical predictions of molecular and sidegroup reorientations, we have associated the depolarized Rayleigh scattering spectra of polypropylene glycol with the segmental motion of polymer backbone. The relaxation times for dilute solutions were found to be larger than those for concentrated solutions. The relaxation times were also found to be independent of the molecular weights of the polymer. The depolarized Rayleigh scattering results were also compared with other types of relaxation studies.

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